Conventionally, there is suggested an illumination apparatus capable of transmitting a signal by modulating an intensity of illumination light. The signal from the illumination apparatus is received by a receiving unit having a photodiode or a general-purpose image sensor, so that information can be transmitted from the illumination apparatus to the receiving unit. Such communication is referred to as “visible light communication”.
In the visible light communication, a special device such as an infrared ray communication device or the like is not required. Power can be saved by using a light emitting diode (LED) as a light source. Therefore, it is attempted to use the visible light communication for a communication system in facilities such as an underground shopping center, a store and the like.
Japanese Unexamined Patent Application Publication No. 2014-35716 discloses an example of a visible light communication apparatus for performing the above-described visible light communication. The visible light communication apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2014-135716 can easily change a modulation degree of a signal changing an impedance (resistance) of an impedance element connected to an LED light source and a power source. Accordingly, even if an illumination design is suddenly changed immediately before a lighting device is installed, for example, an adequate visible light communication environment can designed without exchanging impedance elements.
In a known visible light communication apparatus, modulation degrees of LED light source series having a common rated current can be set to desired levels by single modulation circuit. However, different types of LED light sources having different rated currents cannot be dealt with a single modulation circuit.